A hollow solder wave differentiates over the other types of solder wave in that it projects from a nozzle which may be a slit or, in some cases, one or more apertures, generally directed in one direction, and forms a cavity under the trajectory of the wave. The hollow solder wave is sometimes referred to as a solder fountain. The other types of solder wave flow up out of a nozzle and follow guides back into a solder reservoir. They do not project out of the nozzle in a trajectory such that a cavity is formed beneath the solder wave.
One example of a hollow solder wave, referred to as a solder fountain, is disclosed in U.S. Pat. No. 3,216,642 to De Verter. Other types of hollow solder waves are disclosed in U.S. Pat. Nos. 3,190,527 and 3,705,457 to Tardoskegyi.
In some wave soldering devices, two solder waves are arranged side-by-side. In many cases one of the solder waves flows out of the nozzle into trays or guides. One such nozzle produces a non-turbulent solder wave and is known as the Lambda type solder wave, disclosed by Elliott in U.S. Pat. No. 3,921,888. The second solder wave may be a similar to the first solder wave or, in some cases, may be a hollow solder wave. Examples of two solder waves, one being a hollow solder wave, is disclosed in U.S. Pat. No. 4,465,219 to Kondo and U.K. Patent 1,099,330 to Phillips Electronic and Associated Industries Limited. There are a number of reasons for two solder waves including speeding up the solder process, thus permitting circuit boards to be conveyed at higher speeds through the solder wave, ensuring that solder from the waves contacts all metallized surfaces on the circuit boards and reducing the probability of not soldering some joints as for example discrete chip capacitors or resistors glued to the bottom of a surface mount assembly board.
Over the years the types of printed circuit boards and other components to be soldered have changed. Pins and holes between components and boards are closer together, thus problems of bridging, which was overcome when spacings were greater, is occurring again due to the miniaturization of components mounted on circuit boards. Furthermore, there is always a requirement to speed up soldering circuit boards while, at the same time, avoid bridging or icicles occurring. One problem with a hollow solder wave solder is excessive splashing that occurs after the solder wave jets out from the nozzle, and curves over to fall back either into the reservoir or onto a deflector. This splashing action can cause dross to form on the surface of the solder in the reservoir, particularly when soldering occurs in air. Some present day soldering devices blanket the solder wave with a shield gas that substantially eliminates oxygen and this tends to reduce dross forming on the surface of the solder reservoir. However, there is still a requirement to reduce dross in soldering devices that apply solder in air. Excess dross is undesirable, wasteful, costly and exposes maintenance workers to lead or lead oxides which are present in the dross.